Earth

Earth is the third planet from the Sun and the only place known to support life. Around 71% of its surface is covered by liquid water, and a protective atmosphere of nitrogen and oxygen shields the surface and keeps temperatures mild.

Earth has one large natural satellite, the Moon, whose gravity drives the tides and helps stabilise the planet's tilt — and with it, the seasons.

Earth is also the yardstick every other planet page here is measured against. Its radius of 6,371 km, surface gravity of 9.81 m/s² and mass are the “1 × Earth” that Mercury’s 0.055 and Jupiter’s 317.8 are quoted against, and its orbit defines the astronomical unit — so when Mars is listed at 1.524 AU, that means half as far again from the Sun as we are, and Neptune’s 30.069 AU means thirty times as far.

The 24-hour rotation and the 365-day orbit in the table above are the day and the year that every other figure on this site is converted into. The mean surface temperature of 15 °C is the reason the comparison matters: it sits between Venus at 464 °C and Mars at −63 °C, inside the narrow band where water stays liquid rather than boiling away or freezing solid. A single large moon, an atmosphere thick enough to hold heat but thin enough to see through, and a stable axial tilt are the rest of that balance.

To see where Earth is in its orbit at this moment, open the 3D solar system simulator, which places the Sun and all eight planets at their real heliocentric positions and lets them run in real time.